Method and apparatus for reducing noise and detecting electrode faults in medical equipment

Abstract

A method and apparatus for reducing noise and detecting electrode faults in a physiological activity acquisition system. The method includes the act of delivering a carrier signal through an electrode connected to a subject. Once the carrier signal is delivered, a combined signal having an electrical-activity portion and a carrier-signal portion is sensed by at least one signal sensing electrode attached to the subject. A low-pass, finite impulse response filter, having a first zero point frequency substantially the same as the carrier signal, separates the carrier signal portion from the electrical activity portion. An impedance value for the sensing electrode is calculated using the carrier signal portion. The calculated impedance value is compared against a known value to determine whether an electrode fault exists.

1. A method of identifying an electrode fault in a system designed to measure electrical activity of a subject, the method comprising:
 delivering a carrier signal to the subject by connecting a first electrode to the subject; 
 sensing a combined signal having an electrical-activity portion and a carrier-signal portion by attaching at least one signal sensing electrode to the subject; 
 processing the combined signal detected by the sensing electrode by dividing the electrical activity portion from the carrier signal portion; 
 calculating an impedance value for the at least one signal sensing electrode; and 
 determining whether the calculated impedance for the at least one sensing electrode exceeds a predetermined value. 
 
   
   
     2. A method as claimed in  claim 1 , further comprising reducing high-frequency noise of the electrical activity portion of the combined signal. 
   
   
     3. A method as claimed in  claim 1 , wherein processing the combined signal detected by the sensing electrode includes filtering the combined signal in a low-pass filter with a first zero point frequency, and wherein the carrier signal has a frequency substantially the same as the first zero point frequency. 
   
   
     4. A method as claimed in  claim 3 , wherein the low-pass filter is a finite-impulse response filter. 
   
   
     5. A method as claimed in  claim 4 , wherein the low-pass filter has a cut-off frequency of about 150 Hz. 
   
   
     6. A method as claimed in  claim 4 , wherein calculating an impedance value involves using the carrier-signal portion. 
   
   
     7. A method as claimed in  claim 1 , wherein the combined signals are sensed by attaching multiple sensing electrodes to the subject. 
   
   
     8. A method of identifying an electrode fault in a system designed to measure electrical activity of a subject, the method comprising:
 delivering a carrier signal to the subject by connecting a first electrode to the subject; 
 sensing a combined signal having an electrical-activity portion and a carrier-signal portion by attaching at least one signal sensing electrode to the subject; 
 filtering the combined signal detected by the at least one signal sensing electrode with a low-pass filter having a zero point frequency; and 
 calculating the frequency of the filtered carrier-signal portion based on the zero-point frequency of the low-pass filter. 
 
   
   
     9. A method as claimed in  claim 8 , further comprising:
 identifying an impedance value for the at least one signal sensing electrode; and 
 determining whether the calculated impedance for the at least one sensing electrode exceeds a predetermined value. 
 
   
   
     10. An apparatus for detecting an electrode fault, the apparatus comprising:
 a signal processor; 
 a carrier signal generator; 
 at least one physiological activity electrode to sense a signal and coupled to the signal processor; 
 a carrier signal electrode coupled to the signal processor and the carrier signal generator; and 
 a filter to remove a carrier signal from the signal sensed by the at least one physiological electrode,
 wherein the filter is a low-pass filter, and 
 wherein the low-pass filter is a finite impulse response filter with a first zero point frequency. 
 
 
   
   
     11. An apparatus as claimed in  claim 10 , wherein the low-pass filter is used to determine the characteristics of the carrier signal. 
   
   
     12. An apparatus for detecting an electrode fault, the apparatus comprising:
 a carrier signal generator operable to generate a carrier signal having a frequency; and 
 a signal processor operable to be coupled to at least one physiological activity electrode and a carrier signal electrode, the at least one physiological activity electrode operable to sense a signal having an electrical activity portion and a carrier signal portion, the signal processor having a filter operable to reduce high frequency noise in the signal and to separate the carrier signal portion from the electrical activity portion, the filter having a first zero point frequency that is substantially the same as the frequency of the carrier signal. 
 
   
   
     13. The apparatus as claimed in  claim 12 , wherein the filter is a finite impulse response filter with corner frequency of 150 Hertz. 
   
   
     14. The apparatus as claimed in  claim 12 , wherein the carrier signal electrode is connected to the right leg of a subject. 
   
   
     15. The apparatus as claimed in  claim 12 , further comprising:
 a visual alarm activated by an electrode fault signal from the signal processor. 
 
   
   
     16. The apparatus as claimed in  claim 12 , further comprising:
 an audible alarm activated by an electrode fault signal from the signal processor.